Inertia charge intake manifold for multi-cylinder internal combustion engine and connecting method for branch pipes of intake manifold

ABSTRACT

An inertia charge intake manifold is associated with an internal combustion engine having a plurality of cylinders. The intake manifold includes a plurality of elongated separate branch pipes each corresponding to a respective one of the cylinders. The intake manifold also includes a common flange for connecting a first end of each branch pipe to the internal combustion engine. The common flange has a first surface attached to the internal combustion engine. Further, the intake manifold includes a surge tank to which a second end of each branch pipe is connected. The common flange, the surge tank and each branch pipe are made of a hard thermoplastic synthetic resin. The common flange is integrally connected to the surge tank.

This application is a division of Ser. No. 09/386,445, filed Aug. 31,1999, now U.S. Pat. No. 6,283,078.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an intake manifold in a multi-cylinderinternal combustion engine wherein the manifold is designed tosuper-charge an air-fuel mixture by an inertia effect. The presentinvention also relates to a connecting method for branch pipes of suchan intake manifold.

2. Description of the Related Art

An inertia charge intake manifold includes a surge tank and a pluralityof branch pipes for connecting the surge tank to the cylinder head of amulti-cylinder internal combustion engine. Each of the branch pipesneeds to be relatively long for utilizing the inertia effect of the gasflow for supercharging. Further, all of the branch pipes need to besubstantially equal in length for equalizing the inertia effect withinthe respective branch pipes.

JP-U-1(1989)-99965 discloses an inertia charge intake manifold which ismade of a metal such as aluminum or suitable alloy. The intake manifoldincludes a surge tank located remote from the cylinder head of amulti-cylinder internal combustion engine, and a plurality of relativelylong branch pipes connecting the surge tank to the cylinder head. Thesurge tank is located remote from the cylinder head to provide a longpath for arranging the relatively long branch pipes without sharplybending.

However, since the surge tank is located remote from the cylinder head,the engine combined with the intake manifold becomes inevitably bulky.Further, difficulty arises in supporting the surge tank on the engineparticularly in view of the fact that the surge tank itself must supportother intake components such as a throttle body or carburetor which isrelatively heavy. Indeed, a large tough support bracket is necessary forthis purpose, which results in an increase of cost and weight. Stillfurther, since the conventional manifold is made of aluminum forexample, the branch pipes tend to have rather rough inner surfaces whichmay cause the flow resistance within the branch pipes to becomeunfavorably high.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide anintake manifold which is capable of eliminating or at least reducing theproblems of the prior art described above.

Another object of the present invention is to provide a method ofconnecting the branch pipes of an intake manifold to a surge tank or toa common flange.

According to the present invention, there is provided an inertia chargeintake manifold in an internal combustion engine having a plurality ofcylinders. The intake manifold includes:

elongated separate branch pipes each corresponding to a respective oneof the cylinders;

a common flange for connecting a first end of each branch pipe to theinternal combustion engine; and

a surge tank to which a second end of said each branch pipe isconnected;

wherein the common flange, the surge tank and said each branch pipe aremade of a hard thermoplastic synthetic resin, the common flange beingintegrally connected to the surge tank.

In the above arrangement, since the common flange and the surge tank areintegrally connected to each other, the surge tank is directly supportedby the common flange. Thus, the intake manifold as a whole can bereduced in size, as compared with the conventional intake manifold.

Further, according to the above arrangement, the overall weight of theintake manifold is advantageously reduced, since the common flange, thesurge tank and the respective branch pipes are made of a resin material.In addition, with the use of a resin material, the inner surfaces of therespective branch pipes can be rendered smoother than is conventionallypossible, thereby reducing the flow resistance within each branch pipe.

According to a preferred embodiment, the surge tank may have an externalside surface, and the common flange may be arranged to extend generallyin parallel to the external side surface of the surge tank.

With such an arrangement, the connection area between the surge tank andthe common flange can be rendered comparatively large. In this manner,it is possible to increase the strength by which these two members arebonded to each other.

Preferably, said each branch pipe may be bent so that the first end ishorizontally oriented and the second end is upwardly oriented. Thehorizontally-oriented first end may be fitted into a connecting boreformed in the common flange, while the upwardly oriented second end maybe fitted into a receiving bore formed in an underside surface of thesurge tank.

With such an arrangement, each branch pipe can hold on to the commonflange and the surge tank without using fixing means such as anadhesive.

Preferably, the first end of said each branch pipe may be integrallyformed with a cylindrical protrusion which is nonremovably fitted into aconnecting bore formed in the common flange. The common flange may beprovided with a connection surface attached to the internal combustionengine. The connection surface may be provided with a circular hollowportion extending around the cylindrical protrusion of said each branchpipe. The circular hollow portion may be arranged to accommodate aring-shaped sealing member in a manner such that the sealing memberpartially projects beyond the connection surface of the common flange.

Advantageously, the first end of said each branch pipe may be providedwith a brim coming into contact with the common flange.

According to a second aspect of the present invention, there is provideda method of connecting an end of a branch pipe of an intake manifold toanother member of the intake manifold, wherein the branch pipe and saidanother member are made of a hard thermoplastic synthetic resin. Themethod includes the steps of:

providing the end of the branch pipe with a flat end surface which isgenerally perpendicular to an axis of the end of the branch pipe;

providing said another member with a connecting surface for fixing theflat end surface;

forming a ring-shaped protrusion on at least one of the flat end surfaceand the connecting surface;

arranging a heating wire around the ring-shaped protrusion;

causing the flat end surface and the connecting surface to be pressedagainst each other; and

applying a voltage across the heating wire.

The above method may further comprise the step of arranging aring-shaped seal member made of an elastic material between thering-shaped protrusion and the heating wire. In this method, the voltageapplying step may be performed when the seal member is pressed.

According to a third aspect of the present invention, there is provideda method of connecting an end of a branch pipe of an intake manifold toanother member of the intake manifold, wherein the branch pipe and saidanother member are made of a hard thermoplastic synthetic resin. Themethod includes the steps of:

providing said another member with a connecting bore;

providing the end of the branch pipe with a cylindrical protrusion to beinserted into the connecting bore and with a brim integral with thecylindrical protrusion;

arranging a heating wire circumferentially of the connecting bore;

inserting the cylindrical protrusion into the connecting bore so thatthe heating wire is located adjacent to a boundary between thecylindrical protrusion and the brim of the branch pipe;

causing the brim of the branch pipe and said another member to bepressed against each other; and

applying a voltage across the heating wire.

The present invention will now be described further, by way of example,on the basis of the preferred embodiment given with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a plan view showing a multi-cylinder internal combustionengine provided with an inertia charge intake manifold embodying thepresent invention;

FIG. 2 is a side view showing the same intake manifold as seen in thedirection of arrows II—II in FIG. 1;

FIG. 3 is a fragmentary side view showing principal portions of the sameintake manifold as seen in the direction of arrows III—III in FIG. 1;

FIG. 4 is an exploded view showing the principal portions of FIG. 3;

FIG. 5 is a fragmentary side view showing principal portions of the sameintake manifold as seen in the direction of arrows V—V in FIG. 1;

FIG. 6 is an exploded view showing the principal portions of FIG. 5;

FIG. 7 is a sectional view illustrating a method for attaching a branchpipe to the surge tank;

FIG. 8 is a sectional view taken along lines VIII—VIII in FIG. 7;

FIG. 9 is a sectional view showing the branch pipe connected to thesurge tank;

FIG. 10 illustrates another method for attaching the branch pipe to thesurge tank;

FIG. 11 is a sectional view showing a branch pipe attached to the commonflange;

FIG. 12 is an exploded view showing the portions of FIG. 11;

FIG. 13 is a sectional view illustrating a method for attaching a branchpipe to the common flange;

FIG. 14 is a view taken along lines XIV—XIV in FIG. 13;

FIG. 15 is a sectional view showing a state in which the branch pipe ofFIG. 13 is inserted into the common flange; and

FIG. 16 is a sectional view showing the same branch pipe fixed to thecommon flange.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Preferred embodiments of the present invention will now be describedbelow with reference to the accompanying drawings.

Reference is first made to FIG. 1 illustrating a multicylinder internalcombustion engine which incorporates an inertia charge intake manifoldin accordance with an embodiment of the present invention. In theillustrated embodiment, the engine generally represented by referencenumeral 1 includes four cylinders A1, A2, A3, A4 arranged in seriesalong a crank shaft axis 1 a. The bore axis of each cylinder may extendgenerally vertically, i.e., perpendicularly to the horizontal planecontaining the crank shaft axis 1 a. The engine 1 further includes acylinder head 2 having a corresponding number of intake ports 4, 5, 6, 7each communicating with a respective one of the cylinders A1-A4. Each ofthe intake ports 4-7 is outwardly open at one longitudinal side surface3 of the cylinder head 2.

The cylinder head 2 or the engine 1 as a whole is associated with anintake manifold 8 which mainly includes a surge tank 10 and fourrelatively long branch pipes 11, 12, 13, 14. In the illustratedembodiment, these four branch pipes are separately formed. Each of thebranch pipes 11-14 is attached at one end (which may be called “upperend” below) to a common flange 15 which, in turn, is fixed to thelongitudinal side surface 3 of the cylinder head 2 by bolts 16. In thisway, the branch pipes 11-14 are held in communication with therespective intake ports 4-7. As shown in FIG. 2, the upper ends of therespective branch pipes 11-14 are arranged to extend horizontally.

The surge tank 10, the branch pipes 11-14 and the common flange 15 mayall be made of a hard thermoplastic synthetic resin material such aspolyamide resin (e.g. nylon). With the use of such a resin material, theoverall weight of the intake manifold is made smaller than when a metalmaterial is used.

As shown in FIGS. 1 and 2, the surge tank 10 of the intake manifold 8enters partially under the cylinder head 2 at a portion between the twocentrally located cylinders A2, A3 (the second and third cylinders). Inother words, the cylinder head 2 partially overlaps the surge tank 10horizontally. As a result, the surge tank 10 is arranged adjacent to thecommon flange 15, so that they are integrally connected. The surge tank10 is provided with an outer side surface extending in parallel to thecommon flange 15.

The surge tank 10 is integrally formed with an intake pipe 9 whichprojects upwardly from the upper surface of the surge tank 10 at aposition offset laterally outward from the center thereof. The upper endof the intake pipe 9 is removably connected to a throttle body 17 (FIG.2) which is internally provided with a throttle valve (not shown).

On the other hand, the underside of the surge tank 10 is formed withfour connecting portions 18, 19, 20, 21 for connection to the respectivebranch pipes 11-14 which are generally equal in length. As best shown inFIG. 2, each of the branch pipes 11-14 extends laterally from thelongitudinal side surface 3 of the cylinder head 2 over the surge tank10, then is bent downward to extend at a side of the surge tank 10, thenis bent inward to extend under the surge tank 10, and is finally bentupward to be connected at the other end (which may be called “lower end”below) to a respective one of the connecting portions 18-21 of the surgetank 10.

As shown in the plan view of FIG. 1, the four connecting portions 18-21at the underside of the surge tank 10 are located generally at the fourcorners of a square, rectangle or trapezoid, respectively. The twoconnecting portions 19, 21 disposed closer to the engine 1 arerespectively connected to the two branch pipes 12, 13 extendingrespectively from the second and third cylinders A2, A3 located at thecentral portion of the cylinder series, whereas the other two connectingportions 18, 20 disposed farther from the engine 1 are respectivelyconnected to the other two branch pipes 11, 14 extending respectivelyfrom the first and fourth cylinders Al, A4 located at both ends of thecylinder series.

In this way, each of the relatively long branch pipes 11-14 forconnecting a respective one of the intake ports 4-7 (or the cylindersA1-A4) to a respective one of the connecting portions 18-21 of the surgetank 10 is bent to substantially surround the surge tank 10 which isdisposed close to the longitudinal side surface 3 of the cylinder head2. Thus, compared with the previously described prior art, the manifold8 can be made much more compact. Specifically, the horizontal dimensionL and the vertical dimension H shown in FIG. 2 can be made smaller.

In the illustrated embodiment, the surge tank 10 is arranged close tothe engine 1 beyond the longitudinal side surface 3 of the cylinder head2 in such a manner as to partially enter under the cylinder head 2 by apredetermined amount. This structure additionally contributes to a sizereduction of the manifold 8 combined with the engine 1.

Further, the four connecting portions 18-21 on the underside of thesurge tank 10 are arranged respectively at the four corners of a square,rectangle or trapezoid while the surge tank 10 itself is disposed at acentral portion of the engine 1 along the longitudinal axis la of thecrank shaft. As a result, the length of the surge tank 10 along thelongitudinal axis la of the crank shaft can be reduced.

According to the illustrated embodiment, the two connecting portions 19,21 disposed closer to the engine 1 are respectively connected to the twobranch pipes 12, 13 extending respectively from the second and thirdcylinders A2, A3 located at the central portion of the cylinder series.More specifically, referring to FIGS. 5 and 6, the two branch pipes 12and 13 are integrally formed at their upper ends with cylindricalengaging protrusions 12 a and 13 a, respectively. These protrusions 12a, 13 a are to be fitted into connecting bores 15 a formed in the commonflange 15.

At their lower ends, on the other hand, the branch pipes 12 and 13 areintegrally formed with flanged portions 12 b and 13 b, respectively.These flanged portions 12 b, 13 b are to be fitted into receiving bores19 a and 21 b of the respective connecting portions 19 and 21 of thesurge tank 10. As seen in FIGS. 5 and 6, the central axes of theengaging protrusion 12 a (or 13 a) and the flanged portion 12 b (or 13b) extend perpendicularly to each other.

As shown in FIG. 6, the distance S1 between the center of the connectingbore 15 a of the common flange 15 and the upper surface 23 of thereceiving bore 19 a (21 a) of the surge tank 10 is made slightly largerthan the distance S2 between the center of the engaging protrusion 12 a(13 a) and the upper surface 22 of the flanged portion 12 b (13 b).Thus, in the state where the branch pipe 12 (13) is attached to thecommon flange 15 and the surge tank 10, the latter two components 15 and10 can be held together without using an adhesive or any other fixingmeans.

Similarly, the other two connecting portions 18, 20 disposed fartherfrom the engine 1 are respectively connected to the other two branchpipes 11, 14 extending respectively from the first and fourth cylindersA1, A4 located at both ends of the cylinder series. More specifically,referring to FIGS. 3 and 4, the two branch pipes 11 and 14 areintegrally formed at their upper ends with cylindrical engagingprotrusions 11 a and 14 a, respectively. These protrusions 11 a, 14 aare to be fitted into connecting bores 15 a formed in the common flange15.

At their lower ends, on the other hand, the branch pipes 11 and 14 areintegrally formed with flanged portions 11 b and 14 b, respectively.These flanged portions 11 b, 14 b are to be fitted into receiving bores18 a and 20 b of the respective connecting portions 18 and 20 of thesurge tank 10. As seen in FIGS. 3 and 4, the central axes of theengaging protrusion 11 a (or 14 a) and the flanged portion 11 b (or 14b) extend perpendicularly to each other.

As shown in FIG. 4, the distance S1 between the center of the connectingbore 15 a of the common flange 15 and the upper surface 23 of thereceiving bore 18 a (20 a) of the surge tank 10 is made slightly largerthan the distance S2 between the center of the engaging protrusion 11 a(14 a) and the upper surface 22 of the flanged portion 11 b (14 b).Thus, in the state where the branch pipe 11 (14) is attached to thecommon flange 15 and the surge tank 10, the latter two components 15 and10 can be held together without using an adhesive or any other fixingmeans.

The connecting arrangement of the above embodiment is advantageous forthe following reasons.

For enabling inertia charge of an air-fuel mixture, all of the fourbranch pipes 11-14 must be substantially equal in length. Therefore,each of the branch pipes 11-14 needs to extend along a respective bentpath for meeting this requirement. Further, the two intake ports 5, 6for the second and third cylinders A2, A3 are located closer to thesurge tank 10 than the other two intake ports 4, 7 for the first andfourth cylinders A1, A4, whereas the two connecting portions 19, 21 ofthe surge tank 10 are located closer to the engine 1 than the other twoconnecting portions 18, 20.

On the above basis, it is hypothetically assumed that the two connectingportions 18, 20 disposed farther from the engine 1 are respectivelyconnected to the two branch pipes 12, 13 extending respectively from thesecond and third cylinders A2, A3, whereas the other two connectingportions 19, 21 disposed closer to the engine 1 are respectivelyconnected to the other two branch pipes 11, 14 extending respectivelyfrom the first and fourth cylinders A1, A4. In this case, the downwardlyextending portions of the two branch pipes 12, 13 shift laterallyoutward by as much as the two connecting portions 18, 20 are locatedfarther from the engine 1 than the other two connecting portions 19, 21.As a result, the laterally projecting length L (see FIG. 1) of thedownwardly extending portions of the two branch pipes 12, 13 becomesrelatively large, thereby making the intake manifold 8 bulky.

In reality, however, the two connecting portions 19, 21 disposed closerto the engine 1 are connected to the two branch pipes 12, 13 extendingfrom the second and third cylinders A2, A3, whereas the other twoconnecting portions 18, 20 disposed farther from the engine 1 areconnected to the other two branch pipes 11, 14 extending from the firstand fourth cylinders Al, A4. Therefore, the downwardly extendingportions of the two branch pipes 12, 13 shift laterally inward by asmuch as the two connecting portions 19, 21 are located closer to theengine 1 than the other two connecting portions 18, 20. As a result, thelaterally projecting length L of the downwardly extending portions ofthe two branch pipes 12, 13 is relatively small, thereby realizingcompactness of the intake manifold 8 as a whole.

On the other hand, due to the above-described connecting arrangement ofthe four branch pipes 11-14, each of the two branch pipes 11, 14extending from the first and fourth cylinders A1, A4 must be bent toenter a limited space between the surge tank 10 and a respective one ofthe other two branch pipes 12, 13 under the surge tank 10.

Under this condition, the respective axes of the two connecting portions19, 21 connected to the branch pipes 12, 13 are oriented vertically asshown in FIGS. 1 and 2, whereas the respective axes of the other twoconnecting portions 18, 20 connected to the branch pipes 11, 14 areoriented obliquely at a suitable angle. In other words, the twoconnecting portions 18, 20 connected to the branch pipes 11, 14 areinclined to be directed away from each other. Such inclined orientationof the connecting portions 18, 20 is desirable for the followingreasons.

It is now assumed that the respective axes of the two connectingportions 18, 20 connected to the branch pipes 11, 14 are verticallyoriented substantially in parallel to the respective axes of the twoconnecting portions 19, 21 connected to the branch pipes 12, 13. In thiscase, each of the two branch pipes 11, 14 needs to be bent sharply witha small curvature near the surge tank 10 for entering into the limitedspace between the surge tank 10 and a respective one of the other twobranch pipes 12, 13. As a result, the flow resistance within the branchpipes 11, 14 inevitably increases, consequently providing a hindrance togas feed. Further, a sharp bend of these branch pipes 11, 14 makes amanufacturing process difficult regardless of the fact that they aremade of a resin.

In reality, however, the two connecting portions 18, 20 of the surgetank 10 are inclined at the predetermined angle to be directed away fromeach other for respective connection to the branch pipes 11, 14.Therefore, each of the two branch pipes 11, 14 does not need to be bentsharply for entering into the limited space between the surge tank 10and a respective one of the other two branch pipes 12, 13. As a result,the flow resistance within the branch pipes 11, 14 may be keptrelatively low. Further, these branch pipes 11, 14 may be manufacturedrelatively easily.

With respect to the flow resistance within the branch pipes 11-14, itshould also be appreciated that these branch pipes are made of a hardresin. In this arrangement, the inner surface of each branch pipe isrendered smooth, whereby the flow resistance within the pipe isadvantageously low.

As previously described, the intake pipe 9 of the surge tank 10 isprovided at a position offset laterally outward from the center of thesurge tank 10 (see FIGS. 1 and 3). This offset arrangement of the intakepipe 9 is preferable for removably mounting the throttle body 17 to theintake pipe 9 without interfering with the engine 1.

As can be seen from FIG. 2, the intake pipe 9 may be preferably inclinedor curved in such a way that its axis is directed toward the generalcenter of the square, rectangle or trapezoid defined by the fourconnecting portions 18-21 of the surge tank 10. Such an orientation ofthe intake pipe 9 is advantageous for evenly distributing the air-fuelmixture to the four branch pipes 11-14 while also reducing the flowresistance against the air-fuel mixture. If the intake pipe 9 isarranged offset laterally outward but is not inclined or curved in thisway, the air-fuel mixture supplied through the intake pipe 9 is unevenlydistributed with respect to the four branch pipes 11-14, and a smoothgas flow within the surge tank 10 is hindered to result in an increaseof the flow resistance.

Further, as also shown in FIG. 2, the intake pipe 9 may be preferablyflared toward the interior of the surge tank 10 to have a progressivelyincreasing cross section. This flaring configuration of the intake pipe9 combined with the above-described orientation thereof is additionallyadvantageous for even distribution of the air-fuel mixture with respectto the different branch pipes 11-14 and for a flow resistance reduction.

The throttle body 17 (FIG. 2) is further provided with a conduit (notshown) for introducing blow-by gas from the cylinder head 2 of theengine 1 or purging air from a canister (not shown) at a positiondownstream from the non-illustrated throttle valve.

Reference is now made to FIGS. 7-10 for illustrating a method forconnecting the lower ends of the respective branch pipes 11-14 to theconnecting portions 18-21 of the surge tank 10. For the connectingprocedure, as will be described below, a heat-sealing method mayconveniently be utilized.

First, as shown in FIG. 7, the lower ends 11 b-14 b of the branch pipes11-14 are formed into flat end surfaces 22 so that these flat endsurfaces are perpendicular to the axial lines of the lower ends 11 b-14b. Correspondingly, receiving bores 18 a-21 a are formed at theconnecting portions 18-21 of the surge tank 10. Each of the receivingbores 18 a-21 a is provided with a connecting surface 23 and with acircular protruding portion 24.

Then, a heating wire 25 is put in each of the receiving bores 18 a-21 aso that the wire passes around the protruding portion 24. Then, theheating wire 25 is held between the end surface 22 and the connectingsurface 23, as shown in FIGS. 7 and 8. With the heating wire 25 thusprovided, the branch pipes 11-14 are pressed against the surge tank 10.In this state, a suitable voltage is applied across the heating wire 25for generating heat.

The thus generated heat melts relevant parts of the end surface 22 andthe connecting surface 23 which are pressed toward each other. As aresult, the end surface 22 and the connecting surface 23 will be fusedtogether, leaving the heating wire 25 embedded in the these two surfaces22 and 23, as shown in FIG. 9.

In the above fusing process, melted resin is advantageously preventedfrom flowing inward of the branch pipes 11-14 due to the presence of theprotruding portion 24. Thus, after the branch pipes 11-14 are fixed tothe surge tank 10, there will be no remnants of solidified resinmaterial on the inner surfaces of the branch pipes 11-14.

Differing from the above method, use may be made of an adhesive fornonremovably connecting the branch pipes 11-14 to the common flange 15.

In the illustrated embodiment, the protruding portions 24 are formed onthe surge tank 10. Alternatively, those protrusions may be formed on thebranch pipes 11-14, or on both the surge tank 10 and the branch pipes11-14.

As shown in FIG. 10, the surge tank 10 may additionally be provided witha sealing ring member 26 located between the heating wire 25 and theprotruding portion 24. The ring member 26, which may be made of anelastic soft material, is partially embedded in the surge tank 10, asillustrated. For fixing the branch pipes 11-14 to the surge tank 10, thebranch pipes 11-14 are pressed against the surge tank 10, while apredetermined voltage is being applied across the heating wire 25.

During the above procedure, the ring member 26 is squeezed between thebranch pipe and the surge tank 10. In this manner, unfavorable resinflow into the branch pipes 11-14 is more reliably prevented.

The heat-sealing method described above is also applied for connectingthe branch pipes 11-14 to the common flange 15. In this connection,reference is now made to FIGS. 11-16.

As previously stated, the upper ends of the branch pipes 11-14 areformed with cylindrical engaging protrusions 11 a-14 a which are fittedinto the connecting bores 15 a of the common flange 15. As shown inFIGS. 11 and 12, the common flange 15 has a connecting surface 15 b tobe attached to the longitudinal side surface 3 of the cylinder head 2.On the opposite side of the connecting surface 15 b, the common flange15 has an obverse surface 15 c.

As best shown in FIG. 12, in the connecting surface 15 b, the commonflange 15 is formed with circular hollow portions 27 each of which iscoaxial with a respective one of the connecting bores 15 a. Asillustrated in FIGS. 11 and 12, a sealing member 28, which may be madeof an elastic material such as rubber, is fitted into each hollowportion 27. The sealing member 28 has an axial dimension greater thanthat of the hollow portion 27. Thus, when fitted into the hollow portion27, the tip of the sealing member 28 projects beyond the connectingsurface 15 b of the common flange 15 to a predetermined extent. Withsuch an arrangement, when the common flange 15 is closely attached tothe longitudinal side surface 3 of the cylinder head 2 with the bolts 16(see FIG. 1), the intake ports 4-7 communicating with the branch pipes11-14 are more reliably sealed.

Referring to FIGS. 13-16, the branch pipes 11-14 are fused to the commonflange 15 in the following manner.

As stated above, the branch pipes 11-14 are previously formed withcylindrical engaging protrusions 11 a-14 a. Together with theseprotrusions 11 a-14 a, the respective branch pipes 11-14 are also formedwith brims 11 c-14 c which are integrally connected to the protrusions11 a-14 a, respectively. As shown in FIG. 16, when the branch pipes11-14 are properly attached to the common flange 15, the brims 11 c-14 ccome into close contact with the obverse surface 15 c of the commonflange 15. Such an arrangement is advantageous for enabling accuratepositioning of the branch pipes 11-14 with respect to the common flange15.

As shown in FIG. 13, before the branch pipes 11-14 are inserted into theconnecting bores 15 a of the common flange 15, heating wires 29 arearranged on the obverse surface 15 c so that each heating wire 29surrounds a corresponding one of the connecting bores 15 a (see alsoFIG. 14). In other words, each heating wire 29 is arrangedcircumferentially of the corresponding one of the connecting bores 15 a.With the heating wires 29 thus disposed, the engaging protrusions 11a-14 a of the branch pipes 11-14 are fitted into the connecting bores 15a, so that the heating wire 29 is adjacent to the boundary between theengaging protrusions 11 a-14 a and the brims 11 c-14 c, as shown in FIG.15.

Then, while the branch pipes 11-14 are being pressed against the commonflange 15, a suitable voltage is applied across the respective heatingwires 29 for generating heat. As a result, relevant parts of the branchpipes 11-14 and common flange 15 are melted and fused together, as shownin FIG. 16.

In the above embodiment, the engaging protrusions 11 a-14 a are insertedinto the connecting bores 15 a of the common flange 15. Thus, the branchpipes 11-14 can be firmly connected to the common flange 15. Further,since the heat sealing by using the heating wires 29 is performedoutside of the engaging protrusions 11 a-14 a, melted resin will notflow into the branch pipes 11-14.

As described above, the branch pipes 11-14 are advantageously attachedto the common flange 15 by heat-sealing. Alternatively, it is alsopossible to use an adhesive for nonremovably connecting the branch pipes11-14 to the common flange 15.

In the illustrated embodiment, the intake manifold 8 is connected to thecylinder head 2 of the four-cylinder internal combustion engine 1.However, the present invention is not limited to such an embodiment.

For instance, the present invention may be applied to a three-cylinderinternal combustion engine in which case the underside of a surge tankhas three connecting portions located at the respective corners of anequilateral triangle with one side extending in parallel to thelongitudinal axis of the cylinder head, or to a six-cylinder internalcombustion engine in which case the underside of a surge tank has sixconnecting portions located at the respective corners of an equilateralhexagon with one side extending in parallel to the longitudinal axis ofthe cylinder head.

The present invention being thus described, it is obvious that the samemay be varied in many other ways. Such variations are not to be regardedas a departure from the spirit and scope of the present invention, andall such modifications as would be obvious to those skilled in the artare intended to be included within the scope of the following claims.

What is claimed is:
 1. A method of connecting an end of a branch pipe ofan intake manifold to another member of the intake manifold, the branchpipe and said another member being made of a hard thermoplasticsynthetic resin, the method comprising the steps of: providing the endof the branch pipe with a flat end surface which is generallyperpendicular to an axis of the end of the branch pipe; providing saidanother member with a connecting surface for fixing the flat endsurface; forming a ring-shaped protrusion on at least one of the flatend surface and the connecting surface; arranging a heating wire aroundthe ring-shaped protrusion; causing the flat end surface and theconnecting surface to be pressed against each other; and applying avoltage across the heating wire.
 2. The method according to claim 1,further comprising the step of arranging a ring-shaped seal member madeof an elastic material between the ring-shaped protrusion and theheating wire, wherein the voltage applying step is performed when theseal member is pressed.
 3. A method of connecting an end of a branchpipe of an intake manifold to another member of the intake manifold, thebranch pipe and said another member being made of a hard thermoplasticsynthetic resin, the method comprising the steps of: providing saidanother member with a connecting bore; providing the end of the branchpipe with a cylindrical protrusion to be inserted into the connectingbore and with a brim integral with the cylindrical protrusion; arranginga heating wire circumferentially of the connecting bore; inserting thecylindrical protusion into the connecting bore so that the heating wireis located adjacent to a boundary between the cylindrical protrusion andthe brim of the branch pipe; causing the brim of the branch pipe andsaid another member to be pressed against each other; and applying avoltage across the heating wire.
 4. In an inertia charge intake manifoldfor mounting to an internal combustion engine having a plurality ofcylinders, the intake manifold comprising elongated separate branchpipes each corresponding to a respective on of the cylinders, a commonflange for connecting a first end of each bran pipe to the internalcombustion engine, and a surge tank to which a second end of said eachbranch, pipe is connected, wherein the common flange, the surge tank andsaid each branch pipe are made of a hard thermoplastic synthetic resin,the common flange being integrally connected to the surge tank, a methodof connecting the second end of said each branch pipe of an intakemanifold to the surge tank, comprising the steps of: providing thesecond end of said each branch pipe with a flat end surface which isgenerally perpendicular to an axis of the second end of said each branchpipe; providing the surge tank with a connecting surface for fixing theflat end surface; forming a ring-shaped protrusion on at least one ofthe flat end surface and the connecting surface; arranging a heatingwire around the ring-shaped protrusion; causing the flat end surface andthe connecting surface to be pressed against each other; and applying avoltage across the heating wire.
 5. The method according to claim 4,wherein the surge tank has an external side surface, the common flangebeing arranged to extend generally in parallel to the external sidesurface of the surge tank.
 6. The method according to claim 4, whereinsaid each branch pipe is bent so that the first end is horizontallyoriented and the second end is upwardly oriented, thehorizontally-oriented first end being fitted into a connecting boreformed in the common flange, the upwardly oriented second end beingfitted into a receiving bore formed in an underside surface of the surgetank.
 7. The method according to claim 4, wherein the first end of saideach branch pipe is integrally formed with a cylindrical protrusionwhich is nonremovably fitted into a connecting bore formed in the commonflange, the common flange being provided with a second connectingsurface attached to the internal combustion engine, the secondconnection surface being provided with a circular hollow portionextending around the cylindrical protrusion of said each branch pipe,the circular hollow portion being arranged to accommodate a ring-shapedsealing member in a manner such that the sealing member partiallyprojects beyond the connection surface of the common flange.
 8. Themethod according to claim 4, wherein the surge tank is located centrallyof the engine in a crank axis direction, the common flange having aplurality of connecting portions each for connection to a respective oneof the branch pipes, at least one of the connecting portions of thecommon flange being located closer to a center of this surge tank in thecrank axis direction, at least another of the connecting portions of thecommon flange being located father from the center of the surge tank,said one connecting portion of the common flange being connected to saidone connecting portion of the surge tank via a corresponding branchpipe, said another connecting portion of the common flange beingconnected to said another connecting portion of the surge tank via acorresponding branch pipe.
 9. In an inertia charge intake manifold formounting to an internal combustion engine having a plurality ofcylinders, the intake manifold comprising elongated separate branchpipes each corresponding to a respective on of the cylinders, a commonflange for connecting a first end of each branch pipe to the internalcombustion engine, and a surge tank to which a second end of said eachbranch pipe is connected, wherein the common flange, the surge tank andsaid each branch pipe are made of a hard thermoplastic synthetic resin,the common flange being integrally connected to the surge tank, a methodof connecting the first end of said each branch pipe of an intakemanifold to the common flange, comprising the steps of: providing thecommon flange with a connecting bore; providing the first end of saideach branch pipe with a cylindrical protrusion to be inserted into theconnecting bore and with a brim integral with the cylindricalprotrusion; arranging a heating wire circumferentially of the connectingbore; inserting the cylindrical protrusion into the connecting bore sothat the heating wire is located adjacent to a boundary between thecylindrical protrusion and the brim of said each branch pipe; causingthe brim of said branch pipe and the common flange to be pressed againsteach other; and applying a voltage across the heating wire.